Chandra: Exploring the Invisible Universe

Sources: NASA and Harvard-Smithsonian Center for Astrophysics.

NASA's most powerful X-ray telescope, called the Chandra X-ray Observatory (CXO), was launched from the space shuttle Columbia on July 23, 1999. The spacecraft could remain in orbit for 25–50 years and the scientific mission should last about 5–15 years. Named in honor of the late Indian-American Nobel laureate Subrahmanyan Chandrasekhar, it was formerly known as the Advance X-ray Astrophysics Facility (AXAF).

X-rays are a high energy, invisible form of light. They are produced in the cosmos when gas is heated to millions of degrees by violent and extreme conditions. Much of the matter in the universe is so hot that it can be observed only with X-ray telescopes. The CXO is designed to study some of the great mysteries of the universe such as flaring stars, exploding stars, black holes, and vast clouds of hot gas in galaxy clusters. The telescope has eight times greater resolution and is 20 to 50 times more sensitive than any previous X-ray telescope.

Unlike the Hubble Space Telescope's circular orbit that is relatively close to the Earth, the Chandra X-ray Observatory has been placed in a highly elliptical (oval-shaped) orbit. At its closest approach to Earth, the observatory travels at an altitude of about 9,942 mi (16,000 km). At its farthest, 82,646 mi (133,000 km), it travels almost one-third of the way to the Moon. Due to this elliptical orbit, the telescope circles the Earth every 64 hours, carrying it far outside the belts of radiation that surround our planet. This radiation, while harmless to life on Earth, can overwhelm the observatory's sensitive instruments. The X-ray observatory is outside this radiation long enough to take 55 hours of uninterrupted observations during each orbit. During periods of interference from Earth's radiation belts, scientific observations are not taken.

During 2003, CXO, in conjunction with the Hubble Space Telescope, produced amazing images of the high-energy particles and magnetic fields of the Crab Nebula. The observatory discovered a galaxy with two supermassive black holes and also sent images of our closest supermassive black hole, Sagittarius A. In 2004, CXO reimaged the remnants of Cassiopeia A, which it had first photographed five years previously. The new photos showed bipolar jets reaching about 10 lightyears from the neutron star and revealed that the expanding cloud is rich in iron.

Chandra, along with the Hubble telescope, the Compton Gamma-Ray observatory, and the Aug. 2003-launched Spitzer telescope, is part of NASA's Great Observatories Program, designed to explore the universe by means of visible, ultraviolet, and near-infrared light (Hubble); X-rays (Chandra); gamma rays (Compton); and infrared radiation (Spitzer).